In a number of industries, in particular automotive and aeronautical, a large number of profiles such as tubes are shaped then curved or bent.
These profiles are cut lengthwise, then possibly shaped at the ends and fitted with various components such as nuts, mountings, skirts, etc., and are curved or bent in space depending on precise dimensional features.
At the end of the profile production process, a geometric control of the latter is carried out.
A first method to determine if a shaped or bent profile complies with the required geometric tolerances, consists of using a multi-jointed measuring arm, specialized in measuring bent profiles. This method, which provides numerical measurement results, presents the disadvantage of being a very lengthy method of control and furthermore requires the acquisition of a costly measuring device and the training of skilled operators.
A second method to determine if a shaped and/or bent profile complies with the required geometric tolerances, consists of using a measuring gauge.
This gauge is made of a mechanical assembly presenting an enlarged and partial imprint of the profile fitted with its components and accessories. This imprint is made by means of a series of grooves made in the mechanical assembly, of dimensions corresponding to the profile section added to the positioning tolerance of the profile. The gauge is also designed to allow the profile to be inserted into the grooves of the gauge as well as to be extracted after being controlled.
Such a gauge allows for a quick comparison of the profile to be checked with the shape and circuit defined by the geometry of the gauge. If the profile to be checked can be inserted into the grooves of the gauge naturally, without deforming the said profile, then the latter is considered as complying with the geometric requirements.
Usually, current gauges are made up of a series of aluminum or wooden blocks fixed securely onto a hard, thick plate which is generally made of the same material as the blocks. Furthermore, in these blocks are grooves, often made by machining, or marks with pins added on all or a part of the length of the circuit corresponding to the image of the circuit of the profile to check. The grooves generally have the same height and width measurements as the profile added to the value of the positioning tolerance of the said profile at the level of this groove.
Another way of making these gauges is by welding metal structures together onto a base plate. Parts called guides are machined or fixed, possibly by welding, onto these structures to form grooved parts into which are inserted the profile to check.
The methods of control which consist in using such measuring gauges are all perfectly well-known and mastered by the men skilled in the art, and have the advantage of allowing profiles such as tubes to be checked very quickly.
However, gauges used for the implementation of these controlling methods happen to be very bulky and need large storage areas since, furthermore, they cannot be dismantled and cannot be stacked on top of each other.
Moreover the production processes for these gauges are costly because they are difficult to industrialize and generally need mass machining.
In order to compensate for the latter disadvantage, the U.S. Pat. No. 6,029,333 describes a production process specific to controlling gauge devices consisting of using a single piece of sheet metal held in position by tenons and slots on a base plate, and defines a production process for the gauges by means of CAD and a plate cutting machine.
Although such a production process effectively results in a reduction in production costs as compared to classic production processes, it nonetheless presents, in return, several major disadvantages.
Indeed, firstly in accordance with this process, the achievement of good control gauge assembly accuracy supposes perfect and accurate bending of the sheet. But such bending happens to be very difficult or even impossible to do automatically, and is, in practice, the cause of bending errors, which, if they do not prevent the sheet being mounted onto the plate, result in a deformation of the sheet. In particular, in its upper part which is used to check the profile, the consequence is a perceptible modification of the definition of the circuit of the profile and an impossibility to guarantee gauge assembly accuracy.
Moreover the differential lengthening of the material in the bends generates variations in the unbent part length that could prevent the sheet from being correctly assembled on the base plate, in particular when the profiles to be controlled have numerous bends separated by very short straight parts, such as the rear wheel brake tubing on automobiles. These differential lengthenings of the sheet can lead to it being impossible to assemble the sheet on the base plate and consequently impossible to make the control gauge.
Furthermore, certain profile geometries can lead to making wholly linear shaped sheets that need to be fixed very solidly and permanently on the base plate, in order to ensure that the whole length of the sheets will remain stable and not deform.
Finally, in the case of certain more complex shaped profiles, such as tubing currently found in the automotive industry, this manufacturing process of successively bending a sheet could prove to be impossible to implement due to the general bulkiness by the bending tools.
To sum up, the process of making a gauge as described above can not guarantee respect for tolerances in every profile configuration, is not easy to implement, and offers no solutions for easy assembling and dismantling of the gauge whilst at the same time retaining the tolerance characteristics of it. Moreover, even in the case of dismantling the bent sheet in relation to the base plate, the storage of the gauge proves to be quite difficult, its irregular geometry means that its storage is not free from risk of deformation of the bends.
The U.S. Pat. No. 5,412,877 describes, with reference to FIGS. 23 to 27, another manufacturing process specific to control gauges which consists of making all the components from parts cut out by a laser machine, and of assembling these components by means of a large number of tenons and slots secured by gluing.
Firstly, and in order to provide good rigidity to the gauges, this method of production has the drawback of needing a large number of parts machined as well as a relatively long assembly time for them.
Furthermore the design of the gauge and the way the tenons and slots are fixed on by glue makes the gauge impossible to dismantle. If dismantling were envisaged, it would entail, in fact, a very long and meticulous assembly operation imposing, to prevent any assembly imperfections, a control operation using a three dimensional measuring machine. In addition, a tenon incorrectly driven into one of the slots and its subsequent gluing is always possible, resulting in making a gauge inappropriate to the purpose for which it is destined. In fact, based on the design described, no layout can guarantee that the different parts making up the gauge are stuck together and are consequently positioned correctly.
In practical terms, and in view of the drawbacks aforementioned, it happens that the two above-mentioned methods described in the U.S. Pat. No. 6,029,333 and 5,412,877, with reference to the FIGS. 23 to 30, are almost never implemented in industry, in particular the automotive and aeronautical sectors. In fact it happens that one of the current methods commonly used in the automotive and aeronautical sectors, derives from the method illustrated in the FIGS. 1 to 22 of the U.S. Pat. No. 5,412,877. Nevertheless, marking the trajectories by a laser machine is only used on wooden gauges since as indicated in this patent, this product carbonizes and the marking leaves a deep black visible mark.
The origin of the present invention noticed that current gauges are both heavy and difficult to handle, costly and difficult to make, and difficult to dismantle and re-assemble without damaging the dimensional characteristics of the gauge. Characteristics define the trajectory of the tube to control and for which any deterioration is consequently unacceptable for a control gauge. The objective of the invention is thus to remedy all of these drawbacks.